The invention concerns high-frequency amplifiers, and more particularly a radio-frequency amplifier which constitutes the input stage of a radio transmission system.
Since the signal levels in radio communication devices are subject to fluctuations of considerable magnitude (several tens of dB), it is necessary to adjust the stages following the input amplifier. Especially in the case of portable radio communication devices (e.g. mobile telephones), requirements concerning cost minimization and miniaturization are also important. This demands a simple circuit implementation. In order to accommodate this simple circuit implementation, a reduction in gain by a fixed amount suffices for certain applications. However, it is necessary in this context to ensure that the linearity of the amplifier does not change significantly, especially in the case of high input levels when the overall gain is to be reduced.
Known amplifiers with gain control either work with switchable passive attenuating elements or use electronically controlled attenuating elements (e.g. PIN diodes). In these three-layer diodes, the HF resistance can be controlled by means of a DC current in the forward direction.